Stylesheet/Menu items missing from page type

I'm building my first Silverstripe powered website for a corporate site. I am really enjoying the ease and speed of development, but I've hit a snag: for one page subclass the generated html is missing the stylesheets in the head and menu elements in 'control Menu' template tags.

In my Page.php, I'm using the Requirements::themedCSS calls to include stylesheets. For normal 'pages' and a couple of other page subclasses I have created, this is working fine. For some reason, this particular page type is ditching the CSS and menu items.